Molecular Dynamics and DFT Analysis of Solvation Structures in Hydrated DES and Aqueous Electrolytes

Molecular dynamics (MD) simulations and density functional theory (DFT) calculations can be used to further analyze the molecular structures of the electrolyte in hydrated DES and aqueous solutions. The radial distribution function (RDF) determines the solvation structure of Zn by calculating the probability of various atoms occurring in its vicinity. The highest peaks correspond to the distance between Zn2+ and the element with the highest probability of occurrence. In hydrated DES, the strong interaction between Zn2+ and urea results in the closest peak of urea to Zn2+, indicating that urea enters the primary solvation shell of Zn2+. This peak centered at around 2 ￅ suggests that there is only Zn-H2O interaction in the primary solvation sheath of Zn2+ in the aqueous electrolyte. The significantly higher binding energy of Zn2+-Urea compared to Zn2+-H2O suggests that Urea has a stronger affinity to be part of the solvation sheath of Zn2+ than H2O. MD snapshots of 3 M ZnCl2 clearly show that the majority of the primary solvation shells of Zn2+ are occupied by water molecules, and the system contains an abundance of free water. In comparison, in the DES electrolyte, urea occupies the position near Zn2+. Consequently, breaking the bonds between Zn2+ and Urea requires a significant amount of energy, thereby facilitating homogeneous nucleation during the Zn2+ plating process. These findings are consistent with the earlier spectroscopy analysis. Based on the above, we propose potential solvation structures.